Conventionally, QPW (Quick Pass Write) has been frequently used in a semiconductor storage device such as a NAND flash memory as a data write system. QPW is a system that includes a plurality of write operations and a plurality of verify read operations in one program sequence and repeatedly performs a write operation and a verify read operation, thereby gradually shifting a threshold voltage of a memory cell to a target threshold voltage (hereinafter, “target threshold”).
In such QPW, there is a case where a bit line voltage at the time of a write operation is changed according to the threshold voltage of a memory cell (a type program sequence operation). In this case, to detect the threshold voltage of a memory cell, a plurality of read operations need to be performed in each verify read operation.
However, performing a plurality of read operations for each verify read operation lead to an extended program sequence.